1. Field of the Invention
The present invention relates to a BWA (Broadband Wireless Access) system, and more particularly to an apparatus and a method for providing an MS (Mobile Station) with an MBS (Multicast/Broadcast Service) in a BWA system.
2. Description of the Related Art
As generally known in the art, communication systems have been primarily developed for voice communication services, but they are also evolving to provide data services and various multimedia services. However, conventional communication systems, which are mainly directed to providing voice communication services, still have a narrow data transmission bandwidth and require high subscription fee. For these reasons, they cannot satisfy diversified user demands. Furthermore, in line with rapid development in the communication industry and ever-increasing demands on Internet services, it is important to provide communication systems capable of providing Internet services efficiently. As a result of these trends, BWA systems having a bandwidth large enough to both satisfy the increasing user demands and provide efficient Internet services have been proposed.
In addition to providing voice communication services, BWA systems also aim at supporting various data services both at low and high speeds and multimedia application services (e.g. high-quality moving pictures) in combination. BWA systems are based on wireless media using a broadband of 2 GHz, 5 GHz, 26 GHz, or 60 GHz and are able to access a PSTN (Public Switched Telephone Network), PSDN (Public Switched Data Network), Internet network, IMT-2000 (International Mobile Telecommunications-2000) network, and ATM (Asynchronous Transfer Mode) network in a mobile or stationary environment. In other words, BWA systems are wireless communication systems capable of supporting a channel transmission rate of at least 2 Mbps. BWA systems may be classified into broadband wireless local loops, broadband mobile access networks, and high-speed wireless LANs (Local Area Networks) according to the terminal's mobility (stationary or mobile), communication environment (indoor or outdoor), and channel transmission rate.
The standardization of wireless access schemes of BWA systems is being conducted by IEEE (Institute of Electrical and Electronics Engineers), which is one of the international standardization organizations, particularly by IEEE 802.16 standardization group. Currently, IEEE 802.16d and IEEE 802.16e standards are being established as so to provide stationary or mobile stations with wireless broadband Internet services. Particularly, extensive studies are being made to enable BWA systems, including wireless LAN communication systems and wireless MAN (Metropolitan Area Network) communication systems, to provide high-speed services while guaranteeing mobility and various QoS (Quality of Service). Representative examples thereof include IEEE 802.16d communication systems and IEEE 802.16e communication systems (hereinafter, referred to as IEEE 802.16d/e communication systems).
The IEEE 802.16d/e communication systems are obtained by applying an OFDM (Orthogonal Frequency Division Multiplexing) scheme and an OFDMA (Orthogonal Frequency Division Multiple Access) scheme to the wireless MAN communication systems so that their physical channels support broadband transmission networks. The IEEE 802.16d communication systems do not consider the mobility of SSs (Subscriber Stations), i.e. they assume that the SSs are currently stationary, but consider a single cell structure. In contrast, the IEEE 802.16e communication systems consider the mobility of the SSs. In this regard, SSs having mobility will hereinafter be referred to as MSs (Mobile Stations).
Compared with conventional communication systems for voice communication services, the IEEE 802.16d/e communication systems have a larger data transmission bandwidth. Therefore, they can transmit more data for a limited period of time and share all user channels for efficient channel utilization. Since the QoS is guaranteed, users are provided with various services of different qualities based on the characteristics of services. The IEEE 802.16e communication systems enable all users connected to a BS (Base Station) to share and use common channels, and the base station assigns usable channel sections to respective users for every upward and downward frame. Therefore, the base station must provide respective users with upward and downward access information so that they can divide and use channels for each frame.
To this end, the IEEE 802.16e communication systems divide channels into upward and downward channels and define information regarding each channel in terms of TLV (Type, Length, Value). The TLV is periodically transmitted to all users while being included in a DCD (Downlink Channel Descriptor) message and a UCD (Upward Channel Descriptor) message, so that corresponding MSs are informed of characteristics of the channels.
Meanwhile, the 802.16 communication systems can provide an MBS (Multicast/Broadcast Service) in one of two modes, i.e. a single-BS access mode and a multi-BS access mode, according to how MSs access the service.
In the single-BS access mode, each MS is provided with an MBS from a BS (e.g. serving BS), to which the MS has subscribed. In the multi-BS access mode, each MS is simultaneously provided with an MBS from at least two BSs, for example, both the serving BS and an adjacent BS, in a region where cells of the BSs overlap each other. The network construction of a system for providing an MBS will now be described briefly with reference to FIGS. 1 and 2.
FIGS. 1 and 2 show the construction of a system for providing an MBS in an conventional BWA system. Particularly, FIG. 1 shows the network construction based on a single-BS access mode, and FIG. 2 shows that based on a multi-BS access mode. [PLEASE LABEL “PRIOR ART”]
Referring to FIGS. 1 and 2, the network construction for providing an MBS in a conventional BWA system is based on one of two modes, i.e. a single-BS access mode (FIG. 1) and a multi-BS access mode (FIG. 2), according to how MSs access the service, as mentioned above.
Particularly, according to the network construction shown in FIG. 1, MSs, e.g. first and second MSs 101 and 103, are provided with an MBS from a single BS, e.g. BS 110, to which they belong, in a single-BS mode. According to the network construction shown in FIG. 2, an MS, e.g. a second MS 203, is simultaneously provided with an MBS from two BSs, e.g. a first BS 210, to which it belongs, and an adjacent BS 230, i.e. a second BS 230, respectively, in a multi-BS access mode. FIG. 2 also shows a first MB 201 receiving an MBS from a single BS, i.e. the first BS 210, to which it belongs, and a third MB 205 receiving an MBS from a single BS, i.e. the second BS 230, to which it belongs, in a single-BS access mode.
As such, in the multi-BS access mode, the MBs do not need to subscribe to all BSs, e.g. the first and second BSs 210 and 230, which provide an MBS, in contrast to the single-BS access mode.
In particular, when an MS actually needs a service, it creates a connection for MBS between a corresponding BS and the MS through a service assignment procedure, such as DSA (Dynamic Service Assignment). In this case, the MS receives MBS contents identifier TLV encoding information so as to obtain MBS connection information.
Based on the MBS contents identifier TLV encoding information, the MS can identify the same multicast/broadcast service zone (hereinafter, referred to as MBS_ZONE) with reference to different CIDs (Connection IDs) or different SAs (Security Associations).
Particularly, the MBS_ZONE confirmed by CIDs and SAs refers to a zone having an effective MBS flow. Therefore, the BS broadcasts MBS_ZONE information to the MS via a DCD message, for example. In this regard, it can be said that the MBS_ZONE refers to a group of BSs using the same CID and SA so as to transmit contents.
Meanwhile, in order to provide an MS with an MBS in the multi-BS access mode, it is necessary to equalize the synchronization of information regarding media transmitted by a contents server in the MBS_ZONE, as well as the position of bursts assigned to frames transmitted by BSs. Generally, the fact that the characteristics of media transmitted by the contents server, e.g. characteristics of traffic, are very diversified makes it difficult to properly assign bursts to a number of BSs with regard to each traffic.
However, neither an apparatus nor a method for solving the above-mentioned problems occurring in the prior art has been proposed in the art. Therefore, it is an opportune time to provide a scheme for equalizing the synchronization of media information and the position of bursts so that BSs can efficiently provide MBs with an MBS in a BWA system, as well as a scheme for assigning bursts in accordance with various traffic characteristics.